Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $109.87   11.619%   $122.6358   $122.64   $122.65   $122.60  
  Purchase #2 $212.58   10.639%   $235.1964   $235.20   $235.20   $235.20  
  Purchase #3 $170.47   6.476%   $181.5096   $181.51   $181.50   $181.50  
  Purchase #4 $98.25   11.563%   $109.6106   $109.61   $109.60   $109.60  
  Purchase #5 $202.43   12.842%   $228.4261   $228.43   $228.45   $228.40  
  Purchase #6 $62.43   10.499%   $68.9845   $68.98   $69.00   $69.00  
  Purchase #7 $77.81   10.872%   $86.2695   $86.27   $86.25   $86.30  
  7 purchase totals = $933.84       $1,032.6325   $1,032.64   $1,032.65   $1,032.60